1. Field of the Invention
The present invention relates generally to archery equipment and more particularly pertains to improved bow handles for archery bows.
2. Description of the Prior Art
Archery bows in their basic form include a bow handle, upper and lower resilient limb portions extending therefrom, and a bowstring attached to the upper and lower limbs.
In operation, as the archer draws the bowstring, the upper and lower limbs are flexed and potential energy is stored therein. When the archer releases the bowstring, the stored energy in the limbs propels the bowstring and the arrow nocked thereon forwardly. The greater the energy required to flex the limbs the greater will be the energy available to propel the arrow when the bowstring is released. Arrow acceleration, arrow speed, the distance the arrow will travel, and the force with which it will strike the target are directly related to the force with which the arrow is initially launched.
Compound bows, in general, because of the mechanical advantage obtained through the cam system of such bows, are able to store significantly more energy in their bow limbs than are simple bows. However, the bending moments produced by the relatively widely separated stiff bow limbs of compound bows are large, and commonly require larger, more massive cast, forged or machined handles. Such handles have been typically constructed of lower strength materials such as wood, metallic composites of magnesium, and aluminum, the latter of which are formed by shaping, casting or forging. But because these lower strength materials had to withstand the large bending moments produced by the flexure of the limbs, and since the grip was a portion of the load bearing member, more handle mass was required to achieve the desired strength. An exception was the use of high strength aluminum forgings to produce bow handles. There are disadvantages in producing handles in this manner including the fact that the fabrication process to produce such forgings is expensive.
Since archery bows, particularly those used for hunting, are required to be lightweight and portable, the low strength compound bow handles which require increased size and weight to achieve the desired strength have distinct disadvantages.
On the other hand, the relatively lightweight, high strength aluminum forged handles, capable of operating at higher stress levels, have not, until the recent past, been commercially practical. Handles machined from solid billets of aluminum alloy were introduced a number of years ago. But then the machining process was also time consuming and costly.
As a result machined bow handles made of solid aluminum alloy stock were replaced by cast alloy handles which were far less expensive.
The introduction of less costly CNC (computer numerically controlled) machines for accurately and less expensively machining metal into whatever shape is desired, has made the reintroduction of machined compound bow handles both more cost effective and practical. Such machined metal compound bow handles are presently employed in the more expensive market lines of some bow manufacturers. Bow handles machined of solid metal exhibit better and more consistent material properties than those handles currently produced by sand or die castings.
Many aluminum and aluminum alloys generally, exhibit at least a one-third increase in strength over die cast aluminum or magnesium because they do not have air entrapped in the material that is associated with die cast products. Aluminum, however, is one-third denser than magnesium and provides a substantially stronger bow handle, but one that is heavier. Additionally, machined handles of varying configurations can be fabricated by changing the computer program of the CNC machine at a relatively modest cost.
It has been the practice to reduce the weight of the die cast magnesium handles by coring the areas of the limb mounts and the sight mounting side of the handles within the sight window area. Additional coring has been applied to the handle below the grip on both the sight mounting side and the sight window side.
Another approach to reduce the weight of a bow handle, as described in U.S. Pat. No. 3,923,036 issued to Thomas P. Jennings, et al, is to provide the handle with thin central beam sections formed having thin transverse side and cross rib patterns on the sight window and sight mounting sides of the handle, to stiffen and strengthen the handle. The intersection of the cross ribs and side ribs form recessed void regions in the ribbed surface which are bounded by rigid connections of the cross ribs and side ribs. The weight of the handle is, thus, reduced due to the void regions. The recessed void regions extend in a direction between the sight mounting side and the sight window side of the bow handle but do not extend therethrough to define an opening. This design, by taking advantage of using aluminum alloys of superior strength and employing a minimum of material, provides a lightweight bow handle having a high strength to mass ratio.
Manufacturers of machined billet aluminum bowhandles also seek the produce strong bow handles while reducing the overall weight of the bow. One prior art approach has been to reduce the bow handle cross-section area but in so doing the machined material is subjected to higher bending stresses. Such cross-sections typically comprise configurations that are oval, rectangular or combinations thereof. Such cross-sections exploit good strength properties because they have high moments of inertia about each axis. The cross-sectional material that contributes the most strength is that which is located farthest from the neutral bending axis of the section while the portion contributing least to the strength is closest to the neutral axis. The problem however with solid cross-section handles is their large mass weight. Therefore, in most cases it would be possible to improve the strength to weight ratio of a solid section by removing some of the material nearest the neutral axis of the section.
A known approach to weight reduction has been to form the handle cross-section into a "C", "E", or "I" configuration or variations thereof along the bow handle length with weight reducing holes transversely through the section along the bending axis. A recent solution being used, which is embodied in bows sold by Alpine Archery, PSE Archery, York Archery and Indian Archery includes machining out openings of various shapes through the handle from the sight mounting side and in the direction of the sight window side.